The present invention relates to an optical fiber ribbon twisting device and system for use in the manufacture of fiber optic cables and, more particularly, to a rotatable closing die and a system that uses the same.
Fiber optic cables include at least one optical fiber that can be disposed in a common matrix coating with other optical fibers defining an optical fiber ribbon. Optical fiber ribbons can be formed into a twisted stack for allowing ease of cable bending and maintaining integrity of the ribbon stack. Optical fiber ribbon pay-off devices, for example stranders, are typically used to define a twisted stack, the twist including a lay length or period of twist.
A strander typically includes spools of optical fiber ribbons, which spools are commonly termed packages. Packages can be mounted to a rotating carriage of the strander. In a typical optical ribbon stack manufacturing process, optical fiber ribbons are paid off the packages and directed to a pre-wet closing die, as disclosed in U.S. Pat. No. 5,348,586. The optical fiber ribbons are collected in a closing die that is shaped to receive the stacked ribbons, which shape is typically that of a generally rectangular orifice. Because the journal is mechanically coupled to the strander, the stack is twisted by rotation as it exits the closing die. The next step can be extrusion of a plastic tube about the twisted stack. However, several problems exist with the conventional method. For example, the stack may be mis-aligned with respect to the tube, variation in ribbon lay length can occur, and monitoring of excess ribbon length may be difficult.
The general concept of collecting cable components with a closing die is conventionally known. For example, U.S. Pat. No. 4,765,130, incorporated by reference herein, discloses a method and apparatus for making a cable core with cable core units stranded together while drawing the cable core units along a passline through a closing die and while vibrating the closing die. Vibration of the closing die is intended to facilitate movement of insulated conductors of the cable core units over one another to provide a greater and more uniform packing density of conductors in the resulting cable core. For example, a typical 3600 pair cable is made by stranding together 36 cable core units, each of which comprises 100 individually twisted pairs of insulated conductors stranded together to form a 100 pair cable core unit. During manufacture, the cable core units are passed through a closing die to ensure that the resulting cable core has a uniform diameter and shape. Some insulated conductors do not readily slide over one another during the stranding operation and this can limit the minimum size of closing die that can be used. Consequently, the resulting cable core diameter may be larger than is desired. Moreover, because the insulated conductors do not readily slide over one another the packing density of the conductors may be non-uniform. The solution involves stranding the cable units along a passline through the closing die; and simultaneously vibrating the closing die to compact the stranded elements together.
Other closing die applications are known. U.S. Pat. No. 4,805,392, incorporated by reference herein, describes manufacture of an optical fiber cable in which optical fibers are paid out from packages and inserted into the grooves of a cable core member by means of an inserting head. The core grooves are in the form of an open helix. A photoelectric system is disposed between the packages and the inserting head to provide signals indicating the position of the optical fibers advancing from the packages. A control device is connected to the photoelectric system and is designed to be responsive to the signals generated therefrom to control the speed at which the optical fibers are paid off from the packages. The optical fibers pass through a stationary closing device having holes in a flange fixed on a rigid tubular body through which the grooved core passes. An insertion head, downstream of the rigid tubular body, inserts the optical fibers into the grooves of the core.
The foregoing devices and systems address the need for closing devices in cable manufacture, but do not directly address the problems associated with cable components having at least one optical fiber ribbon therein, in particular, optical fiber ribbons formed into a twisted stack prior to extrusion of a tube thereover. Stationary dies can contribute to undesirable variations in ribbon lay length.
The present invention involves a cable component production line having a rotatable strander for receiving optical fiber ribbon packages thereon; a rotatable closing die sized to receive an optical fiber ribbon stack; and a controller operatively associated with the strander and the closing die for controlling rotation of the closing die, the controller being operative to effect a predetermined rotational ratio between the strander and the closing die whereby a twist can be formed in the optical fiber ribbon stack.
In another aspect, the present invention involves a cable component production line having a rotatable strander for receiving optical fiber ribbon packages thereon, the strander including a closing die coupled to the strander as a source of rotation that at least partially extends into or is proximate a portion of a cross-head containing a grease compound; and a controller operatively associated with the strander, the controller being operative to effect rotation of the strander whereby a twist is formed in the optical fiber ribbon stack within or proximate the the cross-head.
The present invention also contemplates a method of forming an optical fiber cable component employing a strander paying off optical fiber ribbons formed into a stack, the method having the steps of passing an optical fiber ribbon stack through a stack guide independently rotated relative to the strander, forming a twist in the ribbon stack, and passing the twisted ribbon stack through a cross-head and extruding a material thereover.
In another aspect the present invention involves a rotatable closing die for use with optical cable components, the closing die having a stack guide not mechanically coupled to a strander having a ribbon stack aperture therein; and a drive member for rotatably driving the stack guide, whereby rotation of the drive member causes the stack guide to rotate and form a twist in the ribbon stack.